193 lines
11 KiB
HTML
193 lines
11 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>longjmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_program_longjmp skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading">longjmp</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-program.html">program</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<td>
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<div>定义于头文件 <code><setjmp.h></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi c source-c"><span class="kw4">void</span> longjmp<span class="br0">(</span> <a href="c-program-jmp_buf.html"><span class="kw510">jmp_buf</span></a> env, <span class="kw4">int</span> status <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-c11">(C11 前)</span></td>
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<tr class="t-dcl t-since-c11">
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<div><span class="mw-geshi c source-c">_Noreturn <span class="kw4">void</span> longjmp<span class="br0">(</span> <a href="c-program-jmp_buf.html"><span class="kw510">jmp_buf</span></a> env, <span class="kw4">int</span> status <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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</tbody>
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<tbody>
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<tr class="t-dcl-sep">
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<td></td>
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<p>载入先前调用 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 保存的执行环境 <code>env</code> 。此函数不返回。转移控制流到设置 <code>env</code> 的宏 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 的调用方。该 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 会返回作为 <code>status</code> 传递的值。</p>
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<p>若调用 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 的函数已退出（通过返回或通过另一到栈上更高处的 <code>longjmp</code> ），则行为未定义。换言之，只有调用栈间的长跳转是允许的。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-c11">
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<td>
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<p>跨线程跳转（若调用 <code>setjmp</code> 的函数被另一线程执行）亦是未定义行为。</p>
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</td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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</tr>
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</table>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-c99">
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<td>
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<p>若在调用 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 时， <a href="c-language-array.html">VLA</a> 或其他<a href="c-language-declarations.html">可变修改类型</a>变量在作用域中，并且控制流离开了该作用域，则 <code>longjmp</code> 到该 <code>setjmp</code> 将引发未定义行为，即使控制流仍然留在该函数内。</p>
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<p>在上溯栈的途中， <code>longjmp</code> 不会解分配任何 VLA ，若其的生存期以此方式终结，则会出现内存泄漏：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="kw4">void</span> g<span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> a<span class="br0">[</span>n<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// a 仍为已分配</span>
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h<span class="br0">(</span>n<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 不返回</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> h<span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> b<span class="br0">[</span>n<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// b 仍为已分配</span>
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longjmp<span class="br0">(</span>buf, <span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 可能因为 h 的 b 和 g 的 a 导致内存泄漏</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>env</td>
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<td>-</td>
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<td>引用 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 所保存的程序执行状态的变量</td>
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</tr>
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<tr class="t-par">
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<td>status</td>
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<td>-</td>
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<td>要从 <span class="t-lc"><a href="c-program-setjmp.html">setjmp</a></span> 返回的值。若它等于 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> ，则以 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 替代使用</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>（无）</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p><code>longjmp</code> 是有意用以处理未期待的错误条件的，该条件下函数无法有意义地返回。这与其他编程语言中的异常处理相似。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <setjmp.h></span>
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<span class="co2">#include <stdnoreturn.h></span>
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<a href="c-program-jmp_buf.html"><span class="kw510">jmp_buf</span></a> jump_buffer<span class="sy4">;</span>
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noreturn <span class="kw4">void</span> a<span class="br0">(</span><span class="kw4">int</span> count<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"a(%d) called<span class="es1">\n</span>"</span>, count<span class="br0">)</span><span class="sy4">;</span>
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longjmp<span class="br0">(</span>jump_buffer, count<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 将在 setjmp 外返回 count+1</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">volatile</span> <span class="kw4">int</span> count <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 必须为 setjmp 声明 volatile 对象</span>
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<span class="kw1">if</span> <span class="br0">(</span><a href="c-program-setjmp.html"><span class="kw509">setjmp</span></a><span class="br0">(</span>jump_buffer<span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">9</span><span class="br0">)</span>
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a<span class="br0">(</span>count<span class="sy2">++</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">a(0) called
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a(1) called
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a(2) called
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a(3) called
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a(4) called
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a(5) called
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a(6) called
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a(7) called
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a(8) called</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.13.2.1 The longjmp macro (p: 263-264)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.13.2.1 The longjmp macro (p: 244-245)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.6.2.1 The longjmp function</li>
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</ul>
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</dd>
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</dl>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="c-program-setjmp.html"><span class="t-lines"><span>setjmp</span></span></a></div>
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</div>
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</td>
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<td>保存环境<br />
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<span class="t-mark">(宏函数)</span></td>
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</tr>
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</table>
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</div>
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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